The present invention relates to treatment of cardiac valves in a mammalian subject.
Humans and other mammals have a four-chambered heart. Blood from the body flows into the right atrium, and from the right atrium through the tricuspid valve to right ventricle. The right ventricle pumps the blood through the pulmonary arteries to the lungs. Blood from the lungs returns through the pulmonary veins to the left atrium, and flows from the left atrium through the mitral valve, into the left ventricle. The left ventricle, in turn, pumps the blood through the body. As the heart beats, the atria contract to pump the blood into the ventricles, and then the ventricles contract, during a phase of the heart rhythm referred to as “systole,” to pump the blood through the lungs and through the body.
For proper pumping action, the mitral valve must close when the left ventricle contracts. In a disease state known as mitral valve insufficiency, the mitral valve does not close properly, and a significant portion of the blood in the left ventricle is pumped back from the ventricle into the left atrium when the left ventricle contracts. This diminishes the pumping efficiency of the heart. Mitral valve insufficiency is a relatively common condition and afflicts about 4 million people in the United States alone, with about 250,000 new diagnoses of this condition every year. About 50,000 procedures are done every year to alleviate mitral valve insufficiency.
One surgical approach involves implantation of a porcine valve or a mechanical valve in place of the mitral valve. This procedure requires open heart surgery with long recuperation time, and exposes the patient to high risk of complications. Many of the individuals who need mitral valve repair are elderly, which tends to aggravate the difficulties associated with open heart surgery.
Another common surgical approach to repairing mitral valve insufficiency is annuloplasty. In this approach, a wire is wrapped around the mitral annulus, a ring of collagenous tissue surrounding the opening of the mitral valve, to contract the annulus. This improves the performance of the mitral valve. The mitral valve has two major leaves. If the opening of the valve is contracted, as by annuloplasty, the leaves are positioned closer to one another and form a better seal during systole. Annuloplasty as commonly practiced requires a major thoracic surgery with substantial recuperation time and risk of complications.
As disclosed, for example, in U.S. Pat. Nos. 6,306,133; 6,355,030; 6,485,489; 6,669,687; and 7,229,469, it has been proposed to insert a catheter-like device bearing a transducer such as an electrode or ultrasonic transducer into the heart and actuate the transducer so as to heat the mitral annulus, denature the collagen fibers which constitute the annulus, and thereby shrink the annulus. In theory, such a procedure could bring about shrinkage of the annulus and repair mitral insufficiency in much the same manner as traditional annuloplasty. However, all of these proposals have involved positioning of one or more transducers in contact with the mitral annulus during the procedure. It is difficult to provide such accurate positioning of a transducer within a beating heart. Although it is possible to momentarily halt the heartbeat, perform the procedure and then restart the heart, this adds considerable risk to the procedure. Moreover, localized heating of the annulus by a transducer in contact with the annulus introduces the further risk of damage to the epithelial cells overlying the annulus with attendant risk of thrombus formation after surgery.
Perhaps for these reasons, none of these proposals has been widely adopted. Accordingly, prior to the present invention, there has remained a need for a useful and reliable procedure for mitral valve repair.